Heating system circulator pump troubleshooting: here we list & describe other heating system controls that manage or impact heating boiler circulator pump operation.

Troubleshooting & Repair Guide for hot water heating circulator pumps. How to tell if a heating circulator pump is working.

Why do some heating zones work and others not, why does heat come out of zones where thermostats are not calling for heat?

Page top photo: A Taco SR503 zone switching relay that can control multiple heating zone circulator pumps.

This article series discusses Circulator Pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps or circulator pump relay switches and controls.

Circulator Pump Relays: 1 of 3 alternative ways to control hot water heat circulation

• The aquastat is the most common control of heating system boilers.
  
  On a call for heat the thermostat, connected to the aquastat primary control, will operate a single circulator control relay inside the aquastat to turn on the circulator pump, or on some systems the thermostat may be connected to a separate circulator relay discussed just below.
  
  Where there are multiple hot water heating zones fed by multiple circulators, additional circulator relay switches, each operated by a room thermostat for each zone, turn on those additional zone circulators.
  
  (Zone valves, an alternative zone control method, are described later on this page.)
  
  Our photo (aboe-left) shows the interior of a Honeywell R8182D aquastat primary control.
  
  The gray rectangle at top center in this photo is the circulator relay.
  
  You can just make out the red and white thermostat wires connected to the control at the upper left in this picture.
  
  Our page top photo shows the low on a multi-function aquastat or primary control on a heating boiler. The low switch on an aquastat maintains temperature in a heating boiler that also makes hot water using a tankless coil.
  
  The low switch indirectly controls the heating circulator by locking out (keeping off) the circulator pump assembly if the boiler temperature drops into the low range.
  
  Detals are at AQUASTAT CONTROLS - home
• Check valves control circulator flow or flow rate and may be used to balance heating zone flow or heat output.
  
  Details are at CHECK VALVES, HEATING SYSTEM

• Circulator relays on heating boilers -
  
  an older and by some heating service technicians, a preferred method to control the distribution of heat to individual building areas uses a individual circulator pump to force heating water through each individual heating zone piping.
  
  This system too is usually found on hot water baseboard heating systems.
  
  Our photo (above) shows a typical circulator relay with the control's cover removed - thermostat wires are connected at the upper left in this photograph. Line voltage is connected at lower left, and the circulator connections are at lower right.
  
  

  This is a hydronic heating system circulator pump relay control with its cover removed. The basic components and connections in the circulator relay include:

  • Green arrow: Line voltage in - 120VAC power to operate the circultor pump (white and black wires)
  • Blue arrow: thermostat wires - low voltage circuit from thermostat that operates the circulator relay
  • Yellow arrow: 24VAC transformer that operates switches and controls within the relay control assembly
  • Red arrow: the circulator relay switch
  
  Two or more circulator relay switches, one relay for each circulator pump, will be installed to turn on and off each heating water circulator if more than one heating circulator is installed.
  
  Individual low-voltage thermostats located in the living area will respond to a call for heat by switching on the circulator relay which in turns on the (120V) circulator pump.
  
  See RELAY CONTROL SWITCHES for details about how the circulator pump relay operates.
  
  More wiring diagrams that include circulator relays can be downloaded in the manual for your specific circulator pump: if you don't have the manual, download a free PDF copy

  at CIRCULATOR PUMP RELAY MANUALS - below on this page.

• Individual High Limit and Low Limit relay switches On heating boilers: these may be provided on older heating boilers.
  
  See LIMIT CONTROL, SINGLE
• Protectorelays - on older heating boilers a protectorelay or stack relay may be used to control oil burner operation -
  
  see STACK RELAY SWITCH

• Zone valves on heating boilers -
  
  heating water piping in a building, particularly where hot water baseboard heat is used, may be divided into separate heating zones (different floors, or different areas on a single floor) to permit more detailed control of heat distribution in a building.
  
  The control of heating water through these different heating zones may be accomplished by use of zone valves (one per heating zone or area or "loop" of heating piping) which in turn are connected to individual thermostats.
  
  When the thermostat calls for heat in a particular building area, the thermostat switch causes the zone valve to open, to permit hot water to flow through that zone.
  
  When the zone valve is fully open, an "end switch" inside the valve tells the heating system's circulator to begin operating, causing hot water to flow through the zone.
  
  Typically heating systems using zone valves will have two or more zone valves (usually but not always located close to the heating boiler) and a single circulator pump (usually located on the return end of the hot water piping close to the heating boiler).
  
  See ZONE VALVES, HEATING for details.
• Air exit tanks
  
   on heating boilers and circulator pump mounting location - some heating boilers use an air exit tank mounted on the hot water header above the heating boiler to combine the function of
  
  an EXPANSION TANK with
  
  the AIR BLEEDER VALVE or air purge valve to rid the hydronic (hot water) heating system of un-wanted air.
  
  Air in the heating system will often rise to a high loop of radiator or heating baseboard piping where it will block the flow of hot water, leading to an air-bound heating system and no heat in some or all of the heating system.
  
  The air exit tank captures and vents unwanted air from its location above the heating boiler on the boiler outlet or supply side.
  
  When an air exit tank is used instead of a simpler expansion tank at a heating boiler, the boiler manufacturer may specify that the circulator pump be mounted on the boiler outlet side to improve the function of this device. Thanks to Wayne Hoffman, technical advisor for Raypak, a Rheem company that provides hydronic heating equipment, for this detail.

...

Circulator Pump Relay Control IO Manuals

Illustrated above, wiring details for the Taco SR503-4 switching relay, manual given below.

• Also see CIRCULATOR PUMP RELAY CHATTERING
• Also see: aquastats and aquastat relays that also control one or more circulators,
  
  at AQUASTAT CONTROLS  - home
• Honeywell / Resideo: see AQUASTAT L8124 AQUASTAT CONTROL INSTALL / REPAIR as the L8124 aquastsats include a zone circulator relay.
  
  Our Complete List of Honeywell Control Manuals is at HONEYWELL /RESIDEO HVAC CONTROLS & MANUALS
• Taco: See our complete list at TACO DIAGRAMS, MANUALS, PARTS, CONTACT
• Taco SR503-4 SWITCHING RELAY MANUAL [PDF] (2017) (at Taco), Taco Inc., 1160 Cranston St., Cranston RI 02920 USA Tel: 401-942-8000 / Taco (Canada) Ltd., 8450 Lawson Rd. Sutie #3, Milton, Ontario L9T018 Canada Tel: 905-564-9422local copy saved as Taco-SR503-Relay-Manual.pdf
• REHAU INSTRUCTIONS FOR 6 ZONE PUMP RELAY CONTROL [PDF] (2015) (at Rehau) REHAU Building Solutions Ytterbium 4 91058 Erlangen Germany Tel: +49 9131 925700 Mail: erlangen@rehau.com - local copy saved as Rehau-Zone-Relay-Manual.pdf
• Watts Switching Relay 304P Installation & Operation Manual [PDF] (at Watts), local copy saved as Watts-Circulator-Relay-304P.pdf
  
  Excerpt: The Switching Relay 304P connects up to four thermostats and operates circulators to provide heating to a zoned hydronic heating system.
  
  Zone 1 has optional priority over zones 2 through 4 and can be used to provide heat to an indirect domestic hot water tank.
  
  The 304P includes optional exercising to prevent circulator seizure when not in use, and optional post purge operation of the last operating zone to maximize energy savings.
  
  The 304P provides a RoomResponseTM signal to modulating-condensing boilers to optimize comfort while improving boiler efficiency.
• Xylem Ecocirc XL / Ecocirc XL PLUS CIRCULATOR RELAY IO MANUAL [PDF] (at Xylem) - local copy saved as Xylem-Ecocirc-Manual.pdf
  
  Excerpt: The electronic drive described in this manual controls both ecocirc XL and ecocirc XLplus circulators.
  

...

Variable Speed Hot Water Heating Circulator Pumps, Motors & Controls

Shown above is a Bell & Gossett UpStart hot water heating zone circulator pump produced - a B&G product no longer distributed.

Controls for this circulator pump included a knob on the circulator that adjusted a variable-speed circulator motor to select one of speeds operated by a four-speed motor - the circulator output rate could be set by the consumer or heating service technician.

By changing the circulator motor speed we can slow or speed the flow rate of hot water through the zone managed by the circulator.

This provides another way to balance heat flow among multiple zones (and circulators) in a building.

This circulator, the Bell & Gossett SLC-25 Upstart Circulator was sold during the 1980's and is not currently available.

But B&G offered similar replacements (such as the NRF-22) and currently variable speed circulators are available from Taco and Grundfos.

At CIRCULATORS VARIABLE SPEED we describe these products and their controls.

...

Continue reading at CIRCULATOR PUMP WON'T START or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see CIRCULATOR PUMP RELAY FAQs - questions & answers about circulator relays posted originally on this page.

Or see these

Recommended Articles

• BOILER CONTROLS & SWITCHES
• CHECK VALVES, HEATING SYSTEM - flow control valves.
• CIRCULATOR PUMPS & RELAYS - home
  • BELL & GOSSETT B&G EQUIPMENT MANUALS & CONTACT
  • CIRCULATOR PUMP BASICS
  • WHAT GOES WRONG WITH HEATING CIRCULATORS?
  • BYPASS a BAD CIRCULATOR
  • CIRCULATOR COSTS
  • CIRCULATOR NOISES
  • CIRCULATOR PUMP DIAGNOSTIC CHECKS
  • CIRCULATOR PUMP LEAKS
  • CIRCULATOR PUMP MANUALS
  • CIRCULATOR PUMP RELAY CHATTERING
  • CIRCULATOR PUMP RELAY MANUALS
  • CIRCULATOR PUMP MOTOR or BEARING FAILURE
  • CIRCULATOR PUMP MOUNT LOCATIONS
  • CIRCULATOR PUMP MOUNT POSITION
  • CIRCULATOR PUMP RELAYS & OTHER CONTROLS - to control hot water heat circulation
  • CIRCULATOR PUMP RELAY CHATTERING
  • CIRCULATOR PUMP WON'T START
  • CIRCULATOR PUMP WON'T STOP RUNNING
  • CIRCULATOR PUMP RUNS INTERMITTENTLY
  • CIRCULATOR PUMP SPEED SELECTION & ADJUSTMENT
  • CIRCULATORS VARIABLE SPEED
  • MULTIPLE CIRCULATORS HOW TO HOOK UP
  • MULTIPLE HEATING ZONE CONTROL
  • TACO CIRCULATORS & CONTROLS
  • WEAK HEAT, WEAK CIRCULATOR, TOO COOL
• CIRCULATOR PUMPS vs ZONE VALVES
• MULTIPLE HEATING ZONE CONTROL - circulators vs zone valves
• ZONE DAMPERS - warm air heating system zone control.

Suggested citation for this web page

CIRCULATOR PUMP RELAYS & OTHER CONTROLS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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